This disclosure relates to an electron beam vapor deposition apparatus and method for depositing coatings with desirable microstructural orientations on work pieces.
Electron beam vapor deposition devices are known and used for depositing coatings, such as ceramic coatings, onto work pieces. For instance, airfoils for use in turbine engines may include ceramic coatings to protect an underlying metallic alloy from corrosion during engine operation. In some instances, there is a desire to form the coating with a columnar microstructure that is generally perpendicular to the underlying surface. The columnar structure increases the durability of the coating. However, available deposition processes are not practically economic or are incapable of depositing a suitable coating with the desired orientation on all surfaces of a work piece.
Generally, EB-PVD involves using an electron beam to melt and evaporate a source coating material. The evaporated material condenses on the work piece. However, EB-PVD is typically limited to depositing the coating on line-of-sight surfaces of the work piece that face toward the source coating material. EB-PVD is generally incapable or inadequate for depositing the ceramic coating on non-line-of-sight surfaces or surfaces that are steeply angled relative to the source, such as fillet portions of an airfoil or areas between paired turbine vanes.
Another process known as electron beam directed vapor deposition (EB-DVD) has more recently been used to deposit ceramic coatings on non-line-of-sight surfaces. Generally, EB-DVD is somewhat similar to EB-PVD except that a stream of carrier gas is used to carry the evaporated coating material from the coating material source toward the work piece. EB-DVD is capable of depositing the coating with the desired columnar structure on non-line-of-sight surfaces or in between the difficult to access areas, such as between airfoils of paired turbine vanes. However, the use of the carrier gas in EB-DVD adds significant expense to the process.